A Simulation Study to Quantify the Relief Effects on the Observations Performed by Microwave Radiometers

A simulation study to quantify the influence of the topography on the measurements performed by a satellite microwave radiometer is accomplished in this work. The Northern Italy region (including Alps) is considered and the information on the relief, extracted from a digital elevation model (DEM), is exploited. We have developed a simulator of satellite microwave radiometric observations of mountainous scenes operating at different frequencies and observation angles. The simulation shows that the changes in the local observation angle generally tend to decrease the antenna temperature. The effect of the rotation of the polarization plane attenuates (for horizontal polarization) or enlarges (vertical polarization) this decrease. Facets illuminated by radiation from surrounding elevated terrain enhance their brightness temperature with respect to surfaces which scatter atmospheric downward radiation. At horizontal polarization, this results in a general overestimation of the brightness temperature with respect to that measured observing a flat terrain. At vertical polarization, both under and overestimation may occur.